Therapeutic strategies for multiple sclerosis (MS) are essentially based on the use of immunomodulatory agents such as interferon b and glatirmere acetate, but their efficacy is quite limited, they are not well tolerated and they have a very high cost. Recent works showed an immunomodulatory effects of HMG-CoA reductase inhibitors (the so-called "statins"). In experimental allergic encephalopathy, a murine model of MS, statins inhibit the onset and progression of the disease through a shift from Th1 towards Th2 cytokine production. Other in vitro studies suggest the ability of statins to inhibit the lymphocyte migration through the blood brain barrier. Furthermore, in an open labeled human study in MS, statin regimen was associated with a decreased lesional activity assessed by MRI. Statins are well tolerated drugs, used for many years, with a low cost and with a putative efficacy in MS. The investigators suggest to test the pravastatin safety and efficacy on MRI criteria in a double-blind, placebo-controlled study in 40 patients with a relapsing-remitting MS.